Provided is an apparatus for measuring the ammonia concentration in exhaled breath and a method for measuring the ammonia concentration in exhaled breath. The apparatus comprises a sample collection portion, capable of capturing exhaled breath to control the volume of exhaled breath, a pressure gauge for the control of the flow rate of exhaled breath, a small diameter inner tube oriented in a perpendicular direction to the colorimetric sensor to focus the exhaled breath stream onto the central region of the sensor, and an analysis portion capable of receiving said exhaled breath from said sample collection portion. The analysis portion comprises a colorimetric sensor comprising an active component on a substrate. The colorimetric sensor changes color proportional to the ammonia concentration in said exhaled breath.